I see now how you are mounting it, but just a flat plate at the bottom would still work with a washer in the slot and a bolt through.. very small parts like that, having to print it on end (because of the lugs) are difficult because plastic does not have time to cool as it is building up.
Also the slots where the switches are mounted don't need to be there (that little channel could be filled in).
What size bolt holes are they for the switches. Clive